It is frequently required to provide a plurality of different supply voltages for different parts of an electronic circuit. For example, one or more low voltage supplies of the order of 1.8, 1.5, or 1.2 volts may be required for high-speed ICs (integrated circuits) and one or more higher voltage supplies of the order of 2.5, 3.3, or 5 volts may be required for input-output functions. In order to provide the different supply voltages, for example on a printed circuit board (PCB) on which the electronic circuit may be implemented, it is known to provide a plurality of DC point-of-load (POL) or power supply modules on the PCB. For efficient operation and relatively low power dissipation, the DC power supply modules typically comprise switch mode DC-DC converters, but they may alternatively comprise linear voltage regulators, or a mix of converters and regulators.
The supply voltages produced by the power supply modules are typically required to track one another in a predetermined manner. For example, on power-up, simultaneous, ratiometric, or offset tracking may be desired for each power supply module until its output voltage reaches its respective set-point. Converse supply voltage tracking may be required for power-down.
It is known to provide relatively complex arrangements that can control DC power supply sequencing and can perform other power management functions such as monitoring. Such arrangements may be more sophisticated and expensive, and may require more connections, than desired in many applications of DC power supply modules, and also may require undesired programming for their operation.
It is also known to provide a DC power supply module with a control pin referred to as a track pin. In this case, the output voltage of the DC power supply module is limited to the lesser of the set-point of the power supply and a control voltage supplied to the track pin. The track pins of a plurality of such power supply modules can be connected together and supplied with a suitable control voltage to facilitate tracking of the different output voltages produced by the power supply modules during power-up and/or power-down. For example, the control voltage can be provided by a supervisory IC, by the output voltage of another power supply, or by an internal or external resistor-capacitor (RC) circuit.
However, such an arrangement does not provide for tracking of the output voltages produced by the DC power supply modules in the event of fault conditions. For example, in the event of a fault causing an output voltage of one power supply module to decrease rapidly to zero, this known track pin arrangement does not similarly reduce the output voltage of each other power supply module. In addition, the known arrangement does not ensure that all of the power supply modules start operating at substantially the same threshold level of input voltage.
Accordingly, there is a need for an improved method and apparatus which can provide for tracking of DC power supply module output voltages under power-up and power-down conditions and can also accommodate fault conditions.